Preliminary studies on associated bacteria and fungal load of Artificially cultured Clarias Gariepinus burchell 1822 fingerlings
Bacteria and fungi associated with cultured Clarias gariepinus Burchell fingerlings were studied. One thousand (1000) 4-week old fingerlings (5.5 ± 1.1 g) collected from NIFAGOL fish farm, Ile-Ife, were cultured for 6 months in three large concrete tanks (6.0m × 5.0m × 1.2m) and three small concrete tanks (1.5 m × 1.5 m × 1.2m) at the rate of 150 fingerlings per tank. During the study, the fish were fed 40% crude protein based diet at the rate of 3% of the fish body weight per day, 6 days a week. Physico-chemical parameters of water as well as the bacterial and fungal flora were determined on the fish body parts and the culture water. Analyses showed that mean values for temperature, pH and total alkalinity in smaller culture tanks (31.4±0.40 C; 7.7±0.1 and 122.8±10.4 mgL-1 respectively) were higher than values recorded in larger culture tanks (29.4±0.50C; 7.6±0.1 and 114.8±9.0 mgL-1respectively), though not significantly (P>0.05). Conversely, the mean values for dissolved oxygen, biological oxygen demand and organic matter contents were higher in the large culture tanks (5.7±1.0 mgL-1 ; 3.1±0.5 mgL-1 and 11.4±1.6 mgL-1 respectively) than in smaller culture tanks (4.8±0.8 mgL-1 ; 2.4±0.3 mgL-1 and 10.2±1.5 mgL-1 respectively). The mean total mesophilic bacteria count (TMB) of water in the large culture tanks (5.20±0.78 cfu/ml) was significantly lower (P<0.05) than those of small culture tanks (6.08±0.70 cfu/ml). Also, the TMB of the stomach contents of fingerlings cultured in small tanks (10.95±0.99 cfu/g) was significantly higher (P<0.05) than those of fingerlings cultured in large tanks (9.72±0.13 cfu/g). The total fungal count (TFC) on the skin of the fingerlings cultured in small tanks (3.04±1.05 cfu/g) was significantly higher (P<0.05) than those on the skin of fingerlings cultured in large concrete tanks (1.76±0.87 cfu/g). Generally, 12 bacterial and 10 fungal species were found either in the culture water, on the skin, gills of fish and the stomach contents. Pseudomonas sp., P. aeruginosa, Aeromonas hydrophila, Shigella sp., Proteus vulgaris and Staphylococcus aureus were found in the water column as well as the fish parts examined. The dominant fungal isolates identified were Cladosporium sp., Microsporium sp., Trichophyton sp., Aspergillus sp., Botrytis sp., and Mucor sp. The low mortality rate during the period of study showed that Clarias gariepinus is hardy and uniquely suited to cope with the high microbial load present in the culture environment.
Keywords: Bacteria, Fungal, Clarias gariepinus, Culture media